This invention relates to a motor actuator for an air conditioning system which is particularly adapted for use in automotive vehicles.
Conventionally, an air conditioning system for use in automotive vehicles is generally equipped with various driven devices such as a damper for selecting recirculated air and fresh air, a compressor for compressing refrigerant to be delivered to a cooler unit, an air-mix damper for mixing dehumidified cold air from the cooler unit with warm air from a heater unit at such a ratio as to obtain a desired air discharge temperature, and mode selector dampers for selecting vent mode, bilevel mode, foot mode, and defrost mode.
An air conditioning system of this kind for automotive vehicle is, for example, constructed as shown in FIG. 1:
A recirculated/fresh air selecting damper 4 is provided between a recirculated air inlet 2 and a fresh air inlet 3 which are both arranged at an upstream end of a duct 1. The recirculated/fresh air selecting damper 4 is controlled by a first motor actuator 5 to selectively close the inlet 2 and the inlet 3. The air from the recirculated air inlet 2 or the fresh air inlet 3 is introduced into the duct 1 by a blower 6. An evaporator 7 of the cooler unit, an air-mix damper 8, a heater core 9 of the heater unit, mode selector dampers 10 and 11 are arranged in this order in the duct 1 downstream to the blower 6.
The evaporator 7 together with a compressor 12, a condenser 13, a liquid receiver 14, and an expansion valve 15 constitutes a refrigeration cycle. A driving force is transmitted to the compressor 12 from an engine pulley 16 via an electromagnetic clutch 17.
The air-mix damper 8 is for adjusting the ratio at which the cold air from evaporator 7 and the warm air from the heater core 9 are mixed, and is controlled by a second motor actuator 18. A water cock 19 is automatically opened and closed in response to the movement of the air-mix damper 8 such that the air heating rate of the heater core 9 is adjusted.
The mode selector dampers 10 and 11 are for selecting and adjusting the direction and amount of the air blown into the passenger compartment through an upper outlet 20, a lower outlet 21, and a defrost outlet 22. The dampers 10, 11 are controlled by a third motor actuator 23.
A control unit 24 is adapted to control the first motor actuator 5, the second motor actuator 18, the third motor actuator 23, a blower motor 6a for driving the blower 6, and the electromagnetic clutch 17, and comprises a blower control circuit 25, a compressor control circuit 26, a mode selector damper control circuit 27, a recirculate/fresh air selecting damper control circuit 28, and an air-mix damper control circuit 29. Further, the control unit 24 is adapted to receive signals from an air conditioner switch 30, a temperature setter 31, a discharge rate setter 32, an air discharge mode setter 33, a recirculated/fresh air selector mode setter 34, an automatic control setting switch 35, a fresh air temperature sensor 36, a recirculated air temperature sensor 37, an evaporator temperature sensor 38, etc.
However, in an air conditioning system of this kind, the necessity of providing various electric control circuits including the blower control circuit 25 causes the circuit construction to be very complicated, and in the case where these control circuits are composed of semiconductor elements, there is a fear of erroneous operation of the control circuits caused by thermal influence, noise from outside, etc.
In order to solve this problem, an arrangement has been proposed by Japanese Provisional Patent Publication (Kokai) No. 58-20969, wherein the controlling of the motor actuator for the air-mix damper 8 which directly influences the temperature in the passenger compartment is taken as the control basis such that a switch device is composed of a movable contact movable in response to movement of the air-mix damper 8 and a plurality of fixed contacts arranged opposite the movable contact, and various driven devices such as the air blower other than the air-mix damper are controlled in response to an output signal from the switch device.
However, in controlling the blower for example, in response to an output signal from such a switch device, the angular position of the output shaft of the actuator for causing the movable contact to slide on the fixed contacts is in fixed correspondence with the position of the fixed contacts, so that there occurs no hysteresis in the angular position of the output shaft with respect to the position of the fixed contacts between the time the movable contact slides from a fixed contact corresponding to a lower blower rotational speed to a fixed contact corresponding to a higher blower rotational speed, and the time the movable contact slides in the opposite direction. As a result, when the air-mix damper is operated in the vicinity of a blower speed change-over position, change-over of the blower speed takes place frequently, causing hunting in the rotation of the blower, which leads to unstable rotation of the blower and results in uncomfortable feeling to the passengers.
A switch device as described above is typically composed, as shown in FIG. 2, of a movable contact 42 provided on a lower side face of an output gear 41 rotatable by a motor 39 via a speed change device 40 and fixed contacts 45 provided on a printed circuit board 44 fixed on an actuator casing 43.
However, only one such conventional switch device is provided in the proposed conventional air conditioning system, which causes the construction of the control circuit of the air conditioning system to be complicated. Furthermore, since the switch device is provided on an upper side face of the circuit board 44, fixed contacts 45 have to be provided on the upper side face of the circuit board 44, this necessitates that the circuit board 44 should be a costly double-sided printed board because contacts to be connected with a connector, for example, are provided on the lower side face of the circuit board 44 whereas the fixed contacts 45 are provided on the upper side face of same. This disadvantage with the switch device arrangement is derived from a limited space within the air conditioning system, in which the actuator is to be arranged.
Further, another disadvantage with the switch device is penetration of grease for gear lubrication into the switch device, which is caused by the arrangement that the switch device is on the upper side face of the circuit board 44.